This invention relates to gear assemblies and gear drive systems, and more particularly to gear drive assemblies configured to reduce or to eliminate backlash.
Considerable amounts of backlash may exist in conventional gear drive assemblies resulting from clearances between meshing teeth of gears in the drive system. Backlash may be provided in the gears during manufacture to avoid binding or excessive wear in the gear system, or may result from manufacturing tolerances or design criteria for a particular drive system. Backlach may also exist by reason of assembly clearances between bearing surfaces of the gears, shafts, and other members within the gear drive assembly.
In gear drive assemblies desired for use in reversible drive systems, the existence of backlash within the gear drive may not be tolerable, especially where accurate positioning of the drive system is required upon reversal of the direction of drive of the component gear members. Prior art gear drive assemblies configured to reduce backlash include the use of two counteroperating motor drive systems, having the disadvantages of significantly higher cost, and of inducing high internal loading and friction and commensurate excessive gear wear, especially with the use of high output motor drives. Another prior art configuration comprises mounting the drive motor pinion gear on a swingarm, preloading the swingarm and forcing the pinion into the driven gear, which reduces backlash, but at the same time increases friction and strain within the bearings, resulting in a relatively short useful life of the system. Another category of well known antibacklash gear drive configurations utilize split gears, such as disclosed by Bauer (U.S. Pat. No. 3,535,949), Eggins (U.S. Pat. No. 3,545,296), and Sutherland (U.S. Pat. No. 3,512,430), having means to angularly separate the gear teeth of one portion from the teeth of the other portion of the split gear, one portion of the split gear engaging the driven gear on one face of the teeth, and the other portion engaging the other face of the teeth of the driven gear. Relative angular or axial displacement of the two portions may be effected by various means. For example, in one such split gear configuration, one gear portion is fixed to the drive shaft, while the other portion is preloaded by means of a spring to achieve the desired degree of angular displacement of one portion relative to the other. With either direct spring load between the gear portions or with the use of helicoidal splines on the shaft, an inherent disadvantage exists that the preload must be greater than the maximum torque to be transmitted. The result, as in other prior art configurations, is constant high gear tooth loads, high friction, excessive tooth wear, and shortened useful gear life.
The invention described herein eliminates, or substantially reduces in critical importance, the foregoing problems in the prior art by providing a load proportional antibacklash gear drive system wherein a controlled variable force means locks the driving portion of a split gear to the drive shaft, while the other portion floats resiliently controlled by low pressure means into relative angular misalignment with the driving portion to engage both faces of the teeth of the driven gear. In reverse drive, the floating gear portion becomes the driving gear portion while the former driver portion floats in relative angular displacement to prevent backlash. Advantageous attributes of the present invention include the elimination of preload, increased efficiency of drive system operation, reduced friction and tooth wear, and extended tooth life.
The present invention employs two portions of a split pinion mounted on a common drive shaft to deliver torque to an engaged gear. Each pinion portion includes a pressure chamber. Hydraulic or pneumatic pressure moves the pinion portions axially apart and into relative angular misalignment upon engagement of the portions with a collar having V-shaped face teeth. The two pinion portions deliver torque in opposing directions, and therefore, full contact on both tooth faces of the driven gear results. At any given time during operation of the gear drive system of this invention, one of the pinion portions acts as the driver, while the other portion supplies minimum opposing torque to eliminate backlash, which minimizes gear tooth loading. The difference in pressure applied separately to the two pinion portions is proportional to the delivered torque.
The present invention therefore provides an antibacklash gear drive system utilizing a split pinion configuration wherein no mechanical preload on the two pinion portions is required to effect the angular displacement of the two portions sufficient to eliminate backlash, but wherein the applied pressure to effect the displacement is a proportionally controlled function of the applied torque. The applied pressure may be switched hydraulically or pneumatically from one pinion portion to the other upon reversal of the drive system.
It is, therefore, an object of this invention to provide a gear drive system having no backlash in the gears.
It is a further object of this invention to provide an antibacklash gear drive system using a split gear configuration not requiring mechanical preload on the two portions of the split gear.
It is a still further object of this invention to provide an antibacklash gear drive system wherein hydraulic or pneumatic pressure is applied to the split gear portions to effect relative angular displacement of the two portions to eliminate backlash, and wherein the applied pressure is proportional to the torque delivered to the drive system, to minimize gear tooth loading and tooth wear.
These and other objects of the invention will become apparent as the detailed description of certain preferred embodiments thereof proceeds.